Brave Poachers denied a draw
Ricky Drury denied his old club a point with a splendid second half penalty save.
Top scorer Will Britton had given Boston Town the lead after just three minutes.
But Holbeach were soon level and then went ahead early in the second period.
Britton earned the Poachers a spot-kick, only to see it saved by Drury - and Gary Frost's side then ended with 10 men as the striker had to go off injured with all three subs having been used.
Peter Cook had earlier had to come on for Harry Payne in goal to add to the manager's injury worries.
But it was another battling display by Boston, who have now run Newport Pagnell, Holbeach and Leicester Nirvana close, losing by a single goal to all three.